"Solving Coefficient of x^n in Binomial Expansion

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In summary, the conversation is discussing how to find the coefficient of x^n in the binomial expansion of (1-x)^(-6). It is determined that the generalized binomial series must be used since the exponent is a negative integer. The formula is given and it is noted that the coefficient is being asked for when -6-k = n, or when k = -6-n. The conversation then moves on to discussing the general formula for binomial series when n is a positive integer and when it is a fractional or negative value. The question then continues with finding the coefficient of x^6 and x^7 in a given expression.
  • #1
thereddevils
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Homework Statement



Find, in the simplest form, the coefficient of x^n in the binomial expansion of (1-x)^(-6).

Homework Equations





The Attempt at a Solution



i am not sure how to go about with this.
 
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  • #2
are u sure you have to find a cofficient contain x^n?

because u should have a specific value for n, so that you could find the cofficient infront of it, or you should at least have which term you are looking for.
 
  • #3
Willian93 said:
are u sure you have to find a cofficient contain x^n?

because u should have a specific value for n, so that you could find the cofficient infront of it, or you should at least have which term you are looking for.

Yes, that's the question. Maybe it's asking for the coefficient of for any term in the expression.
 
  • #4
Since the exponent, -6, is not a positive integer, you will need to use the generalized binomial series:
[tex](a+ b)^m= \sum_{k=0}^\infty \frac{m(m-1)\cdot\cdot\cdot(m-k+1)}{k!}a^kb^{m-k}[/tex]

Here, of course, a= 1, b= -x, and m= -6 so this is

[tex](1- x)^{-6}= \sum_{k=0}^\infty \frac{-6(-7)\cdot\cdot\cdot(-5-k)}{k!}(-1)^kx^{-6-k}[/tex]

You, apparently, are asked for the coefficient when -6-k= n or when k= -6-n.
 
  • #5
HallsofIvy said:
Since the exponent, -6, is not a positive integer, you will need to use the generalized binomial series:
[tex](a+ b)^m= \sum_{k=0}^\infty \frac{m(m-1)\cdot\cdot\cdot(m-k+1)}{k!}a^kb^{m-k}[/tex]

Here, of course, a= 1, b= -x, and m= -6 so this is

[tex](1- x)^{-6}= \sum_{k=0}^\infty \frac{-6(-7)\cdot\cdot\cdot(-5-k)}{k!}(-1)^kx^{-6-k}[/tex]

You, apparently, are asked for the coefficient when -6-k= n or when k= -6-n.

thanks

Is this answer the most simplified?

[tex]\frac{-6(-7)...(-11-n)}{(-6-n)!}[/tex]

the general formula for binomial series for (a+b)^n is different when n is a positive integer and when n is a fractional or negative value?

[tex](a+ b)^m= \sum_{k=0}^\infty \frac{m(m-1)\cdot\cdot\cdot(m-k+1)}{k!}a^kb^{m-k}[/tex]

Does it matter if the powers(k and n-k) for a and b is swapped since a+b is commutative?

This is the continuation of the question:

Hence, find the coefficient of x^6 and x^7 in (1+2x+3x^2+4x^3+5x^4+6x^5+7x^6)^3
 
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  • #6
any further hints on this question?
 

FAQ: "Solving Coefficient of x^n in Binomial Expansion

What is the binomial expansion?

The binomial expansion is a mathematical concept that involves expanding a binomial expression raised to a certain power. It is used to find the coefficients of each term in the expanded expression.

What is the coefficient of x^n in binomial expansion?

The coefficient of x^n in binomial expansion is the number that is multiplied by x^n in the expanded expression. It is represented by the term nCr, where n is the power of x and r is the position of the term in the expansion.

How do you solve for the coefficient of x^n in binomial expansion?

To solve for the coefficient of x^n in binomial expansion, you can use the formula nCr = n! / (r! * (n-r)!), where n is the power of x and r is the position of the term in the expansion. Simply plug in the values and simplify to find the coefficient.

Why is finding the coefficient of x^n in binomial expansion important?

Finding the coefficient of x^n in binomial expansion is important because it helps in simplifying and solving complex mathematical problems. It also allows for easier manipulation of expressions and helps in understanding the patterns and relationships between terms in an expanded expression.

Can the coefficient of x^n in binomial expansion be negative?

Yes, the coefficient of x^n in binomial expansion can be negative. This can happen when the terms in the expanded expression have alternating signs or when the power of x is an odd number. However, the coefficient is always a whole number, either positive or negative.

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